This invention relates to a rotary cooling roller of a machine for producing a film or sheet of cellophane, polyethylene, aluminum foil, paper or the like, resin finishing machines, laminating machines and extrusion laminating machines for bonding or laminating two or more films or sheets of material, or bonding or laminating different kinds of film or sheets to add properties such as higher strength, heat resistance, water resistance, for example.
In the prior art, for example when paper and synthetic resin films are bonded together to form a strong paper, the conventional cooling machine uses a cooling roller 20 of the type shown in FIG. 5. In the cooling roller 20 of FIG. 5, a water channel 23 is formed between concentric inner and outer cylinders 21 and 22. The cylinders have a space between them which forms a water channel, and a spiral guide partition 24 is mounted in the water channel. Rotary joints 25 are used at the ends of the rotary shaft and have water passages in them, to allow water entering from a cooling water inlet 26 to flow through in a spiral path through the channel and out of a cooling water outlet 27.
In a typical process, thermally melted synthetic resin is flowed down on the raw material paper, and a film of the resin and raw material paper are pressed and bonded together by the nip or pressure application portion between said cooling roller 20 and a pressure roller (not shown) installed next to said cooling roller. While moving over the surface of the cooling roller 20, the synthetic resin is cooled to harden it and to maintain a certain degree of flexibility. Then the product is taken up by a take-up roller (also not shown).
In the aforementioned cooling process, a problem may arise if the synthetic resin is not evenly cooled because the adhesive strength may be unevenly distributed or the surface condition may be defective. Hence the cooling roller must have the function of evenly and efficiently cooling the entire periphery along the full length of the roller.
In the cooling roller having the aforementioned construction, however, the difference in temperature between the inlet cooling water and the outlet cooling water has a direct effect on the surface temperature of the roller, and it is difficult to achieve an even cooling across its width. It is then necessary to control the difference of the cooling water temperature within a narrow range. This poses such a problem that a large quantity of cooling water is required to flow through the roller. Even if the difference of the temperature between the inlet cooling water and the outlet cooling water is kept small, the improvement in heat transfer between the cooling water and the roller surface is limited, and the difference in temperature of the roller surface in the direction of its width has not been improved significantly. It, therefore, is desirable to provide a roller which assures a more even cooling temperature distribution.
In the aforementioned construction, the heat transfer is effected by forced convection, and the heat transfer coefficient is low. Furthermore, as the heat transfer surface is easily fouled, the heat transfer performance is lowered further. To increase the cooling performance, it has been the practice to adopt a large-sized cooling roller, which, however, results in a larger machine size. The problem is not limited to it. Directly above the cooling roll, there are dies from which molten resin flows down in a film form. Because the size of the dies is limited, the distance between the dies and the cooling roller becomes greater, thereby affecting the properties of the product.
Because the size of the product varies from product to product, the cooling roller must be exchanged to meet various standards. Replacement of such a long and large cooling roller is quite troublesome.
As for prior art which is similar to evaporation cooling, the Japanese Utility Model Publication No. 58-49489 discloses a heat pipe roller. In its construction, an inner cylinder having a heater is provided with wick. The roller is used as a fixing roller of an electrophotographic machine, and is exclusively for heating, and cannot be used for cooling which is the objective of the present invention.